What is one question would you like to ask a time traveler from 1000 years in the future?
or
What is one question you would like to ask a time traveler from 1000 years in the future?
English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English. It only takes a minute to sign up.
Sign up to join this communityBoth would you and you would can be grammatical, but only in different specific constructions.
Without is:
✔ What one question would you like to ask a time traveler from 1000 years in the future?
✘ What one question you would like to ask a time traveler from 1000 years in the future?
With is:
✘ What is one question would you like to ask a time traveler from 1000 years in the future?
✔ What is one question you would like to ask a time traveler from 1000 years in the future?